Exhaust muffler comprising a catalytic converter

ABSTRACT

A catalytic muffler for an internal combustion engine of a portable working tool, e.g. a chain saw or a trimmer, having a housing designed to be directly attached to an exhaust port of an engine. The housing further includes a front chamber and a rear chamber divided from each other by an intermediate baffle. The housing further having an inner housing having a first open end constituting the exhaust gas inlet located in the rear chamber. The inner housing includes a catalyst body through which essentially all exhaust gas flows when in use. A second open end of the inner housing is arranged in one of said front and rear chambers and the exhaust gas outlet of the muffler is arranged in the other chamber such that treated gas in use flows through at least one aperture in the intermediate baffle from one chamber to the other.

TECHNICAL FIELD

The several embodiments disclosed herein relate_to a catalytic mufflerfor an internal combustion engine of a portable working tool, e.g. achain saw or a trimmer. The catalytic muffler comprises a housingdesigned to be directly attached to an exhaust port of an engine. Thehousing further comprises a front chamber and a rear chamber dividedfrom each other by an intermediate baffle.

TECHNICAL BACKGROUND

Various exhaust gas mufflers have been known in the art. One of theissues when developing exhaust gas mufflers is to provide adequatecatalytic treatment of the exhaust gas at a low gas counter pressure. Asolution is disclosed in U.S. Pat. No. 6,393,835 that relates to anexhaust gas muffler on an internal combustion engine in motor chain saw.The exhaust gas muffler includes a housing that is assembled of twohousing shells. The one housing shell has an exhaust gas inlet and theother housing shell has an exhaust gas outlet. An inner wall as well asa catalytic converting element is provided in the inner space of themuffler housing. The catalytic converting element is mounted between theexhaust gas inlet and the exhaust gas outlet. In order to ensure anadequate catalytic converting treatment of the exhaust gas at low gascounter pressure, it is provided to divide the entering exhaust gas flowand to conduct at least one of these component flows in contact with thecatalytic converting element. The component flows are brought togetherand mixed with other before exiting from the muffler housing. However,not all exhaust gas is treated and the construction is relativelyspacious.

In U.S. Pat. No. 5,732,555 a catalytic converter is disclosed fortreating the exhaust gases of an internal combustion engine which isless expensive and easier to manufacture than other catalyticconverters. This multi pass catalytic converter/muffler uses a singlecatalytic support bed without increasing the overall size of thecatalytic converter/muffler. The outer surface area of the catalyticsupport bed is disposed adjacent to the outer wall of the catalyticconverter housing, with only the mat in between. Secondary air may beprovided upstream before the exhaust gases make their first pass throughthe catalytic support bed, or after the first pass but before the secondpass or even after the second pass. Again, the construction isrelatively large.

An invention to reduce high exhaust emission output levels is disclosedin U.S. Pat. No. 5,521,339, describing a muffler for coupling to anexhaust port of an internal combustion engine which includes a housing,a first hollow body within the housing, a catalyzer within the firsthollow body, and a second hollow body within the housing. The firsthollow body has an inner surface defining a first chamber and an inletadjacent the exhaust port to admit the exhaust gas into the firstchamber. The exhaust gas is exothermally treated as it flows through thecatalyst in the first chamber in a direction away from the engine andpasses through an outlet of the first hollow body to a second chamber.The second chamber is formed by an inner surface of the second hollowbody and an outer surface of the first hollow body. The treated exhaustgas flows through the second chamber in a direction toward the engineover the outer surface of the first hollow body where a thermal reactiontakes place and/or further emission reduction takes place by a catalyticcoating on the outer surface of the first hollow body. The treatedexhaust gas passes through an outlet of the second hollow body to athird chamber. The third chamber is formed by an outer surface of thesecond hollow body and an inner surface of the housing. After expandingand mixing in the third chamber, the exhaust gas is expelled from thethird chamber through an outlet of the housing adjacent the engine. Thevolume downstream of the catalyst is however small resulting in hightemperatures in the catalyst. The thermal endurance of catalysts isnormally low.

EP 1 600 613 discloses a muffler for attachment to an engine thatincludes an inlet for receiving exhaust gases into the muffler, acatalyst assembly located within the muffler, and a fastener tube forfastening the muffler to the engine. A fastener tube cover covers thefastener tube and includes an outlet for exiting exhaust gases. Theoutlet includes a directional louver that directs the exiting exhaustgases. The fastener tube cover can retain a spark arrestor, whichmaintains maximum spark particle size in the exiting exhaust gases. Oneissue with this muffler is length of life for the catalyst resultingfrom high temperatures.

SUMMARY OF THE INVENTION

One object of the several embodiments of the_present invention is toprovide an improved catalytic muffler for a combustion engine to reducesome of the above-related problems.

According to several embodiments, a catalytic muffler is provided_for aninternal combustion engine of a portable working tool, e.g. a chain sawor a trimmer, comprises a housing designed to be directly attached to anexhaust port of an engine. The housing further comprises a front chamberand a rear chamber divided from each other by an intermediate baffle.The housing further comprises an inner housing having a first open endconstituting the exhaust gas inlet located in the rear chamber. Theinner housing comprises a catalyst body through which essentially allexhaust gas flows when in use, wherein the second open end of the innerhousing is arranged in one of said front and rear chambers. The exhaustgas outlet of the muffler is arranged in the other chamber such thattreated gas in use flows through at least one aperture in theintermediate baffle from one chamber to the other. The heat exchange inthe muffler provides for a lower output temperature from the muffler.The contact with the outer wall of the housing further cools down thegas after passage through the catalyst.

Preferably, the second open end of the inner housing is arranged in thefront chamber, i.e. when_in use the exhaust gas that flows through thecatalyst body continues into the front chamber in said housing. At leasta first part of the inner surface of the front chamber constitutes apart of the outer wall of the housing and a second part is theintermediate baffle with at least one aperture. The intermediate baffleseparates the front chamber from the rear chamber. The rear chamber hasat least a part of its inner surface constituting a part of the outerwall of the housing. The rear chamber comprises an outlet for thetreated exhaust gas and the rear chamber preferably at least partlysurrounds the exhaust gas inlet such that during use there is acounterflow heat exchange between the exhaust gas in the inlet upstreamof the catalyst body and the treated exhaust gas. Thus, the cooling ofthe gas leaving the muffler is improved

In an alternative embodiment, the second open end of the inner housingis instead arranged in the rear chamber, i.e. when in use the exhaustgas that flows through the catalyst body continues into the rear chamberin said housing. According to this embodiment, the rear chamber willhave the highest temperature allowing the gas to cool down on its wayinto the front chamber and also being further cooled before it leavesthe front chamber. Thus, for the user, this embodiment provides for amuffler that has an outside surface temperature of the muffler, thelarger part facing the user that is lower than in the other embodimentwhere the second open end of the inner housing is arranged in the frontchamber.

Preferably, the at least one aperture in the intermediate baffle islocated adjacent the housing of the catalytic muffler. This aperture orapertures are arranged close to the inner surface of the housing andthereby controlling the gas to flow close to the inner surface of thehousing in order to maximize the convection of heat for cooling the gas,i.e. decreasing the temperature of the gas to a larger extent.

Further, the housing of catalytic muffler preferably comprises twomating parts. The inner housing preferably also comprises two matingparts. Preferably, at least one of these two parts has a recess forfitting the catalyst body. The edges of two mating parts in contact canfor instance be folded to assemble the muffler and/or the inner housing,i.e. neither welding nor soldering is needed, if desired. Of course,welding and/or soldering or any other means of fixing the two matingparts to each other could be used. The recess is preferably arrangedsuch that when assembling the inner housing, the catalyst body is justplaced in the recess of one of the parts and the other part is combinedwith the first part to secure the position of the catalyst body. In analternative embodiment both of the two mating parts have recesses forfixing the catalyst body in a specific position in the inner housing.This specifically applies when the cross section of the catalyst body iscircular. Both of the mating parts should in this case preferably haveequally sized recesses for facilitating mounting or dismounting of thecatalyst body in the inner housing, i.e. to avoid having to force thecatalyst body into one of the parts. Alternatively, one part could beslightly larger, i.e. carry more than half of the catalyst body, forretaining the catalyst body during assembly with a snap like fitting.

In a further embodiment the joint between the two mating parts of theinner housing is arranged such that it in use is in an essentiallyvertical plane perpendicular to the exhaust inlet and the first openend, thus enabling making at least one bend in said plane. Should it bedesired, even a meander shaped inner housing could be designed. In analternative embodiment, a catalytic muffler as described above could bedesigned without an intermediate wall to create two chambers. Instead,several bends of the inner housing could replace the function for heattransfer of the intermediate wall.

For facilitating the production of the exhaust gas muffler according tothe present invention, the intermediate baffle separating the front andrear chamber is preferably a separate part fitted onto a shoulder of oneof the two mating parts at assembly as evident from FIG. 1.

In one preferred embodiment the inner housing comprises a wall upstreamthe catalyst body dividing the flow into two parts. This could be donefor example by simply putting a metal plate in the parting line of thetwo mating parts. This is advantageous from a durability point of viewwhere particles can attach to the plate instead of possibly damaging theengine. Also, the heat radiation from the catalyst body is furtherdecreased since the plate will absorb some of the heat. Alternatively,the upstream plate is arranged perpendicular to the parting line of thetwo mating parts. This upstream plate is then preferably inserted inslots of the two mating parts.

Preferably, the catalytic muffler further comprises a flow directioncontrol part such that the exhaust gas is forced to change directionbetween the exhaust gas inlet and the catalyst. The thermal radiationfrom the catalyst is normally very high and therefore it is advantageousto have a change in the flow direction of the exhaust gases, i.e. suchthat the visibility of the catalyst from the exhaust gas inlet isdecreased in order not to damage any part of the engine. For instance,the change in direction can be provided as a parallel displacement ofthe pipe or simply a bend. In combination with a plate upstream of thecatalyst body and with this change of direction it is possible toeliminate direct heat radiation from the catalyst body to the inlet ofthe muffler and thereby protecting the engine.

In an alternative embodiment the inlet upstream of the catalyst body hasat least one aperture for allowing untreated exhaust gas to enter therear chamber. For some applications there is a need to keep thetemperature further down in the catalyst and therefore a small part ofthe exhaust gas is by-passed.

Preferably, the inner housing is in contact with the intermediatebaffle. For instance, when the second open end of the inner housing isarranged in the front chamber, the passage through the intermediate wallof the inner housing preferably coincides with the part of the innerhousing holding the catalyst body, such that the opening area in theintermediate baffle is maximised and thereby allowing for proper heatconduction. In the alternative embodiment, with the second open end ofthe inner housing being arranged in the rear chamber, the inner housingcould be bent such that it runs parallel with the intermediate baffleand thus also providing a larger contact area and sufficient heatconduction.

BRIEF DESCRIPTION OF THE FIGURES

Exemplary embodiments_will now be further described with reference tothe accompanying figures.

FIG. 1 is a cross section of a catalytic muffler according to oneexemplary.

FIG. 2 is an alternative cross section of the catalytic muffleraccording to the embodiment shown in FIG. 1.

FIG. 3 is a cross section of a catalytic muffler according to analternative embodiment of the present invention.

FIG. 4 is a perspective view of a further embodiment of the catalyticmuffler according to one exemplary embodiment with parts of the housingcut out in order to illustrate the flow pattern.

FIG. 5 is a perspective view of an alternative inner housing accordingto the embodiment of FIGS. 1 and 2.

FIG. 6 is a perspective view of a further alternative inner housingaccording to the embodiment of FIGS. 1 and 2.

DESCRIPTION OF PREFERRED EMBODIMENTS

In FIGS. 1 and 2 a catalytic muffler 101 according to one of theembodiments of the present invention is shown. The muffler 101 comprisesa catalyst body 102 arranged in a inner housing 103 with a first openend 104 and a second open end 105. The exhaust gas 106 from thecombustion engine (not shown) enters the muffler 101 at the first openend 104 of the inner housing 103. The exhaust gas outlet from thecombustion engine is directly attached to the first open end 104 of theinner housing 103. The inlet channel, i.e. the part of the inner housingupstream of the catalyst body 102, is in this embodiment bent twice inorder to minimise the heat radiation from the catalyst body 102 to thefirst open end 104 and thus protecting the engine (not shown) from hightemperatures. The exhaust gas 106 is treated when passing through thecatalyst body 102. The treated gas 107 then exits the inner housing 103at the second open end 105 of the inner housing 103 and enters the frontchamber 108 where the gas is cooled due to heat transfer at housing 109.The treated gas 107 is forced to flow through apertures 110 that arearranged close to the housing 109 in an intermediate baffle 111 in orderto maximise the cooling of the treated gas by convection heat transfer.When passing through the apertures 110, the treated gas 107 enters therear chamber 112. In the rear chamber there is partly a counter currentheat exchange between the exhaust gas 106 entering the muffler 101 inthe inlet channel of the inner housing 103 and the treated gas 107flowing into the rear chamber 112. Thus the treated gas 107 is furthercooled and the exhaust gas 106 is heated prior to entering the catalystbody 102. The efficiency of the catalysis is, due to the heating of theexhaust gases 106 prior to entering the catalyst body 102, thusimproved. In this embodiment tubes 113 are arranged to support thehousing 109 of the muffler 101. The housing 109 of the muffler 101 isfurther divided into two mating parts 114 and 115. The muffler gasoutlet 116 is in this embodiment arranged adjacent the front chamber 108and the treated gas 107 exits the muffler 101 via a passage pipe 117from the rear chamber 112. The contact surface area between the innerhousing 103 and the intermediate baffle 111 is preferably as large aspossible to allow for heat conduction from the inner housing 103 via theintermediate baffle 111 to the housing 109 of the muffler 101.

FIG. 3 shows an alternative embodiment of the catalytic muffler 201. Themuffler 201 comprises a catalyst body 202 an inner housing 203 with afirst open end 204 and a second open end 205. The exhaust gas 206 entersthe muffler 201 at the first open end 204 and passes through thecatalyst body 202. The treated gas 207 exits the inner housing 203through the second open end 205 of the inner housing 203 in the rearchamber 212 (not in the front chamber 208 as compared to the embodimentin FIGS. 1 and 2). The treated gas 207 is forced to flow through theapertures 210 in the intermediate baffle 211. The apertures 210 arearranged close to the housing 209 of the muffler in order to enhance thecooling by convection of the treated gas 207. In this embodiment tubes213 are used to support the housing 209 of the muffler 201. The housing209 of the muffler 201 is further divided into two mating parts 214 and215. The muffler gas outlet 216 is in this embodiment arranged in thefront chamber 108 and the treated gas 107 exits the muffler 101 via thefront chamber 208 and the outlet 216. Compared to the embodiment shownin FIGS. 1 and 2, the rear chamber 212 will hold a higher temperature,i.e. the part of the muffler 201 closest to the engine. This means thatthe front chamber 208 will be cooler and thus more user friendly sincethat part of the muffler 201 is more likely to come into contact withthe user. Also, the inner housing 203 is bent such that the contactsurface area between the inner housing 203 and the intermediate baffle211 is maximised. This is advantageous as regards the heat transfer fromthe inner housing 203 to the intermediate baffle 211. The bent shape ofthe inlet channel of the inner housing 203 minimises the heat radiationfrom the catalyst body 202 to the engine (not shown). In order tofurther increase the contact surface between the inner housing 203 andthe intermediate baffle 211, the joint connecting the two parts makingup the inner housing is preferably made with a flange shaped and sizedto optimize the contact with the intermediate baffle. Preferably thisflange is fitted into a slot arranged in the intermediate baffle,compare FIG. 3 and imagine the flange cutting through the baffle forimproved cooling and increased mechanical stability.

FIG. 4 shows an alternative catalytic muffler 301 according to thepresent invention comprising a catalyst body, an inner housing 303 witha first open end 304 and a second open end 305 allowing the exhaust gas306 to enter the muffler 301 at the first open end 304 flow through theinner housing 303 and the catalyst body. The treated gas 307 exits theinner housing 303 through the second open end 305 of the inner housing303 into the front chamber 308. The treated gas 307 is forced to flowclose to the housing 309 of the muffler 301 as a result of apertures 310being arranged close to the housing 309 in an intermediate baffle 311through which the treated gas 307 flows into the rear chamber 312. Alsoin this embodiment, tubes 313 are arranged in the muffler 301 to supportthe housing 309. The housing 309 is assembled from two mating housingparts 314 and 315. After entering the rear chamber 312 the treated gasexits the muffler 301 through an outlet 316. As in the embodiment shownin FIGS. 1 and 2, there is a counter current heat exchange between theincoming exhaust gas 306 in the inner housing 303 and the treated gas307 flowing mainly in the opposite direction through both chambers. Theinner housing 303 is also divided into two mating parts with a partingline 317.

FIG. 5 shows an example of an embodiment of the inner housing 103, orrather one half of the inner housing 103 with a flow dividing plate 119positioned upstream of the position for the catalyst body (not shown inFIG. 5). An advantage with this flow dividing plate 119 is that thedirect heat radiation from the catalyst body will be decreased since theplate 119 will absorb some of the heat.

In FIG. 6, an alternative embodiment of the flow dividing plate 119′ isshown. This solution is slightly more complex since it requires that aplate is bent instead of just cut as in the embodiment shown in FIG. 5and then positioned in the inner housing 103. The positioning in theinner housing 103 could for instance be carried out by making a slot inthe inner housing 103 in which the plate 119′ is arranged. Just weldingor soldering can be an alternative in order to facilitate themanufacturing. Even though the solution in FIG. 6 is more complicatedfrom a manufacturing point of view, there is an advantage. Compared withthe solution in FIG. 5, the solution shown in FIG. 6 eliminates thedirect heat radiation from the catalyst body to the inlet of themuffler/inner housing 103.

In yet another alternative embodiment, the dividing plates 119 and 119′of FIGS. 5 and 6, respectively, could be combined such the inletupstream the catalyst is divided into four parts (not shown). Anadvantage with this embodiment is that the dividing plate 119′ could beattached to the dividing plate 119 by, for instance, by means of somesort of notch. The dividing plate 119 is, as described above, relativelyeasy to fasten, for instance, as a part of the contacting joint of thetwo mating parts of the inner housing.

Further, the arrangement of the tubes 113, 213, 313 shown in FIGS. 1-4where there is a tube on both sides (one on each side) of the innerhousing 103, 203, 303 allows for alternative design solutions as regardsthe inner housing 103, 203, 303. For instance, the shape of the innerhousing can include additional bends and even be of a meander shaped.

Also, as described with the embodiment in FIG. 3, in order to increasethe contact surface between the inner housing and the intermediatebaffle, the joint connecting the two parts making up the inner housingis preferably made with a flange shaped and sized to optimize thecontact with the intermediate baffle. This is also applicable to theembodiments shown in the other figures.

The foregoing is a disclosure of preferred embodiments for practicingthe present invention. However, it is apparent that device incorporatingmodifications and variations will be obvious to one skilled in the art.Inasmuch as the foregoing disclosure is intended to enable one skilledin the art to practice the instant invention, it should not be construedto be limited thereby, but should be construed to include suchmodifications and variations as fall within the scope of the claims.

1-12. (canceled)
 13. A catalytic muffler for an internal combustionengine of a portable working tool comprising: a housing designed to bedirectly attached to an exhaust port of an engine, the housing furthercomprising a front chamber and a rear chamber divided from each other byan intermediate baffle, said housing further comprising an inner housinghaving a first open end constituting the exhaust gas inlet located inthe rear chamber, said inner housing comprising a catalyst body throughwhich essentially all exhaust gas flows, and wherein a second open endof the inner housing is arranged in one of said front and rear chambersand the exhaust gas outlet of the muffler is arranged in the otherchamber whereby treated gas flows through at least one aperture in theintermediate baffle from one chamber to the other.
 14. A catalyticmuffler according to claim 13, wherein the second open end of the innerhousing is arranged in the front chamber.
 15. A catalytic muffleraccording to claim 13, wherein the second open end of the inner housingis arranged in the rear chamber.
 16. A catalytic muffler according toclaim 13, wherein the at least one aperture in the intermediate baffleis located adjacent the housing of the catalytic muffler.
 17. Acatalytic muffler according to claims 13, wherein the inner housingcomprises two mating parts.
 18. A catalytic muffler according to claim17, wherein the joint between the two mating parts is arranged such thatit is in an essentially vertical plane perpendicular to the exhaustinlet and the first end, thereby providing at least one bend in saidplane.
 19. A catalytic muffler according to claim 17, wherein at leastone of the two mating parts has a recess for fitting the catalyst body.20. A catalytic muffler according to claim 13, wherein the inner housingcomprises at least one dividing plate upstream of the catalyst bodydividing the flow into at least two parts.
 21. A catalytic muffleraccording to claim 13, wherein the inlet upstream of the catalyst bodyis bent.
 22. A catalytic muffler according to claim 13, wherein theinlet upstream of the catalyst body has two bends such that thedirection of flow of the exhaust gas is substantially parallel whenreaching the catalyst body as the direction of flow at the upstream endof the inlet.
 23. A catalytic muffler according to claim 13, wherein theinlet upstream of the catalyst body has at least one aperture forallowing untreated exhaust gas to enter the rear chamber.
 24. Acatalytic muffler according to claim 13, wherein the inner housing is incontact with the intermediate baffle.
 25. A catalytic muffler accordingto claim 13, wherein said portable working tool is a chain saw or atrimmer.